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HISTORY OK THK VEGETABLE KINGDOM. 



with nutritious fluids, that vivify the buds. 

 From the upper part of the stem proceeds a new 

 centre of vegetation, from wliich rises a new 

 shoot, which in its development exliibits tlie 

 same phenomena as the first. To this second 

 shoot succeeds a third, Avhich the following year 

 is surmounted by a fourth, and so on. 



The trunk is therefore found to be formed by 

 a series of very elongated cones, placed upon 

 each other, and having their apex directed up- 

 wards. But the apex of the innermost cone 

 stops at the base of the second shoot, that of the 

 next cone at the base of the third shoot, and so 

 on successively, it being only at the base of the 

 trunk that the number of woody layers corre- 

 sponds to the number of years of the plant. 

 Thus, for example, a stem of ten yeai-s has ten 

 woody layers at its base, but presents only nine 

 at the height of the second shoot, eight at the 

 third, and finally only one at the top. It is for 

 this reason that the trunk of dicotyledonous 

 trees is more or less conical, the number of its 

 woody layers becoming gradually less, as they 

 ascend from the base to the summit. 



There are trees in which this growth in height 

 is very manifest ; as in pines and firs. At the 

 end of the first year, there is seen at the top of 

 the stem a conical bud, from which proceeds a 

 whorl of young branches, at the centre of which 

 is one that rises vertically. It is this branch 

 which is destined to continue the stem. At the 

 end of the second year, there proceeds from its 

 summit a similar bud, which, in its develop- 

 ment, presents the same phenomena. Thus the 

 age of these trees may be known by the number 

 of whorls of branches which they have on their 

 stem. 



Growth of the stem of monocotyledonous trees. 

 If we examine the growth of the stipe of a palm, 

 we find that it takes place in the following 

 manner : — After germination, the leaves, which 

 are generally folded upon themselves, become 

 expanded, and fonn a circular bundle, arising 

 from the neck of the root. From the centre of 

 this bundle there issues, the second year, another 

 tuft of leaves, which push outwards those pre- 

 viously existing. Then the oldest fade, dry, 

 and fall ofi^; but their bases, being firmly fixed 

 to the summit of the root, remain without 

 withering; and, by uniting, fonn a solid ring 

 which becomes the base of the stipe. A new 

 central bud being developed every year, the 

 outcnnost leaves of that which precedes it, fidl j 

 off, and their base fonns a new ring, which is 

 added above those that already existed. 



Such is the development of the stem of mono- 

 cotyledonous plants. Their stipe, in place of 

 being formed of concentric layers, like the trunk, 

 of the dicotyledones, is composed of rings placed 

 one above another. From this it will be seen, 

 that the trunk of the monocotyledones can grow 



but very little in thickness. In fact, its lateral 

 growth can take place only inasmuch as the 

 persistent base of the leaves is not yet suffi- 

 ciently solidified and hardened to resist the 

 outwards pressure which the bud tends to exer- 

 cise upon it. Accordingly, we see that the 

 palms, which sometimes shoot up to a heiglit of 

 120 or 140 feet, have a stem which is often 

 scarcely a foot in diameter. 



In dicotyledonous trees, the cambium is the 

 essential agent by which the enlargement of the 

 stem is effected, as it every year becomes oi'gan- 

 ized, and fomis a new woody Layer. Here, on 

 the contrary, it is the terminal bud which 

 crowns the stipe that performs this office ; and, 

 were this centre of vegetation removed, the tree 

 would inevitably perish. 



If we compare, in a general way, the growth 

 in diameter of the stem of dicotyledonous trees 

 and that of the monocotyledones, we shall find 

 that it differe not less than their anatomical 

 structure. In the dicotyledones there are two 

 distinct systems; the central system, formed of 

 the medullary tube and the woody layei-s, and 

 the cortical sj/stem, which is composed of the 

 bark. These two systems enlarge separately, so 

 that there are two surfaces of growth in this 

 class of vegetables. The central system increases 

 by the new layers which are added to its outer 

 surface, and the cortical system increases by its 

 inner surface. 



In monocotyledonous vegetables, on the con- 

 trary, there is but a single surface of growth, 

 and consequently but a single system ; hence, it 

 may be inferred that the system which exists in 

 these plants, is the cortical, and that the central 

 system is wanting. It follows that the stipe ot 

 tlie palms is organized like the bark of the 

 dicotyledones. 



From these different considerations, it is ob- 

 vious that the stipe of palms, and other woody 

 monocotyledonous vegetables, differs essentially, 

 both in its organization and in its mode of de- 

 velopment, from the tnmk of dicotyledonous 

 vegetables. If we extend this obsei-vation farther, 

 it will be seen that as the stipe differs so much 

 from the trunk, in its origin and mode of 

 growth, it is not surprising that its internal 

 organization, which is merely the result of this 

 mode of development, should equally difl'er from 

 that of the woody stem of dicotyledonous plants. 

 For, let it be recollected, how the stem of an 

 oak, or any other dicotyledonous vegetable, is 

 formed and grows: — the seed germinates; the 

 radicle descends into the ground ; the little stem, 

 or its representative organ, which serves as a 

 support to the gemmule, and raises it above the 

 base of tlie radicle, ascends. At this early period 

 in the life of the plant, the organ which is to 

 constitute the stem already exists under the fonn 

 of a more or less elongated cylinder, composed 



